Implementation of Closed Loop based Scan Mechanism

2015

International Conference on Communication, Control and Intelligent Systems (CCIS)

Implementation of Closed Loop based Scan Mechanism Leo Louis

Ashok Kumar

Saffrony Institute of Technology,

Scientist Engineer, SFED, SEG, SEDA,

Department of Electronics and Communication,

Space Applications Centre, (SAC),

Gujarat Technological University,

Indian Space Research Organization, (ISRO),

Ahmedabad, India

Ahmedabad, India

E-mailld: [email protected]

E-mailld: [email protected]

Abstract-This paper presents a closed loop scan mechanism

With the help of this proposed module, the sensor being

using a stepper motor based Gimbal Technique. For its control,

used would face correct direction accurately. For this, a closed

Arduino microcontroller based drive electronics is developed. This paper proposes a flexible structure for usefulness in various applications

like

tracking,

satellite

imaging

etc.

This

paper

analyzes the programming and hardware structure for an easy implementation using the Arduino microcontroller. For a bipolar stepper motor drive, the full H-bridge driver based electronics is developed. Motor shaft position is sensed by incremental optical encoder. The proposed module has high accuracy (.06% in scan rate). Keywords: Scan Mechanism, Stepper Motor, Motor Driver, Arduino Mega, Rotary Encoder

loop mechanism is used, for continuous monitoring of the acquired encoder data. The sensors are mounted on the Gimbal, which works with the help of a Stepper Motor, which is connected to a microcontroller with the help of a motor controller

/ motor driver [9].

This proposed module also checks whether the Gimbal is working in the desired way; if there is any error in its functioning,

the

program

stored

in

the

microcontroller

automatically rectifies it by sending the appropriate signal pulse to the motor. Here we are using a commercially available

I.

INTRODUCTION

Arduino Microcontroller which is an open source user friendly

The sensors used in the INSAT series of satellites have a point area of scan or a pencil beam of light that are used to scan a wider area. As scan mechanisms are an essential part in the

field

of

Remote

Sensing,

Inertial

Navigation

and

Photography, the sensors used for scanning should be able to

electronic platform with high accuracy and simple features. This platform has been selected due to its low cost and its usage in various automation projects for similar systems. With this project, we will explore how it accurately helps out in the scan mechanism. Results are also discussed.

cover a wider area. II.

Scanning a larger plus a wider area can now be possible

METHODOLOGY

using electrical or electromechanical devices as actuators

For successfully accomplishing and designing this project

which have now become easier with the improvement in

it is divided into five sub tasks; each specifically focusing on the detailed and easy implementation of the project. First we

technology. For a point sensor having a point area of scan or a sensor having a pencil beam of light can only be able to scan larger and wider area with the help of some actuators which can make the sensors have a movement of-xo

--->

+xo. For this type

of rotations here we are using a Gimbal as an actuator for the front end of the sensor. These gimbals can be made up of stepper motors, dc motors or even solenoids. To improve the system accuracy it is operated in a closed loop. The existing scan mechanisms were developed using analog mechanisms, which always had accuracy issues making them not as reliable as this proposed digital system. The

analyzed the different types of motors to select an appropriate motor which has a precise stepping and also a high accuracy for the Gimbal [9]. The second task was to study each hardware precisely, it's working behavior with each other, and to study the steps by which we could proceed with this project. The third task was to design and develop a suitable motor driver for the stepper motor that is capable of micro stepping the motor in the Gimbal for maintaining the accuracy in the directions. The fourth task was to develop the code in the Arduino IDE. Finally, the fifth task was to implement the project by assembling it with all the studied conditions and maintaining its parameters for an easy implementation.

sensors that are being used for sensing should be perfectly

III. DETAILED DESCRlPTION

facing the desired direction and angle, with a high accuracy. This can only be possible, if the sensor is placed or mounted,

The Fig. 1 shows the functional block diagram of this

on such a device, which can have similar movements. For this

system and all its sub-blocks representing the overall flow of

type of mechanism we use the concept of a "Gimbal"[9].

program

978-1-4673-7541-2/15/$31.00 it 20151EEE

control

from the microcontroller to the various

system components i.e. the motor driver, stepper motor and the

The sensor that is mounted on the motor should be facing

rotary encoder. Sensors are mounted on the motor for their

the desired direction at the desired time. A rotary encoder is

appropriate movement.

attached to the motor which continuously updates itself and interrupts the microcontroller with the current position of the motor, which in turn shows the present position of the sensor. These pulses are then in turn used to correct the true position or compensate the error of the motor The microcontroller attends to the interrupt and monitors the data it receives from the output of the encoder Ch A and

Rotary Encoder

Ch B. If it finds any abnormal condition, the microcontroller would rectify it by providing the appropriate pulse to the

Fig. I: System Block Diagram •

Motors:

motor driver to correct it. The control system of the project is shown in the Fig. 3.

For the accurate movement and precise

stepping a stepper motor is used for this module. These

are

driven

by

the

motor

driver

/ motor

controller to which they are connected to. •

Motor Driver / Motor Controller:

The motor driver is

used to drive the motor according to the pulse that it receives from the microcontroller. Here we would be using a L293DNE motor driver

/ motor controller IC

manufactured by the Texas Instruments. •

Rotary Encoders:

Fig. 3: Project Control System

Rotary encoders are devices used

for obtaining the exact angle information about the

IV. IMPLEMENTATION

rotation and the direction of the motor it is connected

This project is divided into two different parts.

to, for data and correction purpose. •

Microcontroller:

The

microcontrollers

•

named

Arduino

"Arduino Mega" is used for collecting the encoder

on

the

motor

face

the

card,

the

motor

driver

motors and the mechanical structure on which it

pulse to the motor driver which would make the mounted

The module of this project consists of the

microcontroller

circuit, the rotary encoder that is connected to the

outputs, analyze them and to the give the appropriate sensor

Hardware:

would be mounted for easy movements.

correct

direction.

•

Software:

The software code which is fed into the

microcontroller would make the hardware's function according to our expectations. This project is built around the Arduino Mega consisting of the AT Mega 2560 microcontroller. A.

Hardware 1.

Motor:

A motor is simply a machine that works on the

principle

of

converting

electrical

energy

into

mechanical energy. Most of the motors function due to the interaction between the motor's winding currents and the magnetic field to generate force within the

Fig. 2: System Diagram

motor during its normal functioning [4][13].

The actual system block diagram with a closed loop

In this project a bipolar stepper motor is used with

digital feedback is shown in Fig. 2. The microcontroller

specifications such as Maximum voltage: 5V DC, Step angle:

obtains the true position of the motor and sends the appropriate

0.90 and Steps per revolution: 200. Due to its ability of rotating

pulse to the motor driver for rotating the motor according to

its shaft in small and precise steps of rotation or in a full rotation

/

the H-bridge logic. These pulses are given according to the

these motors are also used in the positioning of video cameras

desired direction of the motor rotation i.e. in the clockwise or

antennae at extremely low speeds (such as in astronomy),

anti clockwise direction. The motor driver then sends the

positioning of robots, computer peripherals (disk units, plotters,

appropriate pulse to drive the motor connected to it.

printers), space technique and military field etc [6] [15].

310

TABLE2: MOTOR INPUTS UL I 0 I 0 X

Enable I 1 I I 0

3.

Fig. 4: Example of a Stepper Motor

2.

Motor Driver! Motor Controller:

LL 0 1 0 1 X

UR 0 1 I 0 X

Rotary Encoder:

LR I 0 0 1 X

OutDut Clockwise Anti-Clockwise Motor Breaks No Output

A rotary encoder, also called a

shaft encoder, is an electro-mechanical device that

The pulse given out

converts the angular position or motion of a shaft or

from the microcontroller is not enough for the motor

axle to an analog or digital code. An example of

to run. For this purpose we need a motor controller,

Rotary Encoders is shown in Fig. 7. Rotary encoders

commonly known as the motor driver which would

are used in many applications that require precise

receive the input pulse from the microcontroller and

shaft rotation-including industrial controls, robotics,

send its output pulse to the input of the motor [11].

special purpose photographic lenses, computer input

The Motor driver works on the principle of H-Bridge

devices

which helps in rotating the motor in clockwise or anti

(such

as

opto-mechanical

mice

and

trackballs), controlled stress rheo meters, and rotating

clockwise direction [11].

radar platforms [14]. Encoders have outputs namely Ch. A, Ch. B, and Index in which Ch. A and Ch. B are 90 degrees out of phase so are called quadrature outputs. These pulses define the direction of the motor; when Ch. A leads Ch. B it is said to be in the clockwise direction and when Ch. B leads Ch. A it is said to be in

the

anti-clockwise

direction

[14].

Fig.

8

shows

the

quadrature output of a rotary encoder in clockwise direction.

Fig. 5: Using L293D Dual Half H Bridge

Here we use L293DNE a 16 pin DIP type bipolar motor driver IC by the Texas Instrument for driving the Motor. One Fig. 7: An Example of a Rotary Encoders

such IC is capable of driving 2 DC Motors or 1 Stepper Motor at a time. Each input pin is connected to the digital

110 pin of

the Arduino microcontroller [7].

A B

I

�

phase 1

I

I I I I

I

I

121 3

I I I

I I

411 I

I

I I I I

I

I I

I

I

I

I

12 13 I 411

�

I

I I I I

I

I I

I

I

I

I

12 131 41

Fig. 8. Quadrature Outputs of a Rotary Encoder Showing a Leading B [14] TABLE2: OUTPUTS OF THEROTARY ENCODER Channel A OFF-O OFF-O HlGH-I HIGH-I

Fig. 6: Connections with the Microcontroller and an Image of the Motor Driver IC L293 D [71

The microcontroller is programmed in such a way that it gives out pulses that can be given to the motor driver to drive

4.

the motor that is connected to it. These motor inputs viz.

Channel B OFF-O HIGH-I HIGH-I OFF-O

Microcontroller:

Output Position 0 Position 1 Position 2 Position 3

A microcontroller is an integrated

circuit that is used for automation purpose consisting

Upper Left (UL), Lower Left (LL), Upper Right (UR), Lower

of memory, and programmable

Right (LR) are given to the motor according to the H-bridge

110 peripherals [10].

An Arduino card known as "Arduino Mega" consists

logic are shown below in Table 1.

of a microcontroller AT Mega 2560 as shown in Fig. 311

9 is used in this project. It is used to monitor and

which interrupts the microcontroller processing by giving the

rectify the peripheral devices connected to it. There

current position data. The microcontroller on fmding an error

are different types of Arduino cards available [2]; Fig.

sends the appropriate signal pulse to make it more accurate

10 shows an example of one such Arduino card

A portion of the implemented code is as shown below.

known as the Arduino Uno.

This code is used to rotate the motor

void loop () { digitalWrite(a, HIGH); digitalWrite(abar, LOW); digitalWrite(b, LOW); digitalWrite(bbar, HIGH); digitalWrite(a, HIGH); digitalWrite(abar, LOW); digitalWrite(b, HIGH); digitalWrite(bbar, LOW); digitalWrite(a, LOW); digitalWrite(abar, HIGH); digitalWrite(b, HIGH); digitalWrite(bbar, LOW); digitalWrite(a, LOW); digitalWrite(abar, HIGH); digitalWrite(b, LOW); digitalWrite(bbar, HIGH); }

Fig. 9: Arduino Mega 2560 [2]

The Arduino Mega 2560 has an operating voltage of 5v and an input recommended voltage of 7-12V with its input voltage limits ranging from 6-20V. Consisting of 54 digital

110

pins of which 15 provide PWM output and 16 provide analog

V.

110 for digital and analog interfacing respectively, a power The

connector for the power requirements of the Arduino card and

various

RESULTS

experimental

results

performed

for

this

a USB connector for burning the software code into the

system show its accurate system performance. Fig. 11 and Fig.

microcontroller. The USB connector can also be used for the

12 shows its rotated angle and velocity profile respectively.

power requirements by keeping it connected to the Laptop

/

The achieved Velocity error is ;:::: 0.06 RPM at 10 RPM

PC in cases when no power adapters are available [1][3]. It

which is shown in Fig. 13. This velocity is limited by motor

also has a flash memory of 256KB of which 8KB is used by

position of 0.9 degree per step.

the boot loader and SRAM of 8 KB, and EEPROM of 4 KB and a Clock Speed of 16 MHz [1]. The encoder outputs via Ch. A and Ch. B are fed to this card which is continuously monitored and checked for their desired functioning. This software code has been developed in the Arduino IDE using the C language. This code has then been uploaded (fed

/ burned) into the microcontroller memory

using a USB cable provided with the Arduino Card. B.

Software The software portion of this project includes the coding of

the Arduino Microcontroller which is done in C language in the Arduino software also known as the Arduino IDE. This code is required to have an interaction with the motor driver

/

motor controller by providing the appropriate pulse to it for the easy motor rotation [5]. It is also capable of rectifying the errors by continuously Fig. 10: Arduino Uno with Descriptions of the 110 Locations

monitoring the outputs of the rotary encoder Ch. A and Ch. B

312

50 40

•

1

E 20 cu

10

c: c(

0

�

]

•

10

20

30

Elapsed Time (5)

40

project at SAC, to Mr. Sanjeev Mehta, Head of SFED-SEDA

50

for his precious support, to Mr. Arup Roy Choudhury, GD­ SEG and Mr. Saji Kuriakose, Deputy Director of SEDA-SAC

Fig. II: Profile of the Rotated Angle

for their constant encouragement and keen support during the work. The authors are also grateful to the reviewers Dr S.c.

t

Bera and Mr. D.R. Goswami for reviewing this paper and making it more accurate REFERENCES

5

[1] 0

[2] [3]

-5

-10 -15

[4]

II

j

[5]

0

10

20

30

Elapsed Time

(s)

40

50 [6]

Fig. 12: Profile of the Achieved Velocity [7] [8]

[9]

[10] [11] Fig. 13: Profile of Achieved Velocity Error

[12]

VI. CONCLUSION This

microcontroller

HRDD at SAC-ISRO for giving us an opportunity to do our 0

\l cu cu a. II)

the

The authors are grateful to 1. Ravishankar, Head of

-40

e-

of

ACKNOWLEDGMENT

-50

E

architecture

which is used to rectify the motor position in case or

-30

10

software

errors in the functioning.

-10

15

The

allows the continuous monitoring of the encoder data

... 0-20 �

which can also be preprogrammed

according to the user needs.

30

,g;

The Arduino platform performed the predefmed task automatically

paper

presents

the

implementation

[13]

of

scan

mechanism using the Gimbal on an Arduino Mega 2560

[14]

platform. With the implementation of this project, the scan

[15]

mechanisms can be done very precisely. This paper also concludes these various points:

31 3

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